Towards F1 Hybrid Seed Potato Breeding

Abstract

Compared to other major food crops, progress in potato yield as the result of breeding efforts is very slow. Genetic gains cannot be fixed in potato due to obligatory out-breeding. Overcoming inbreeding depression using diploid selfcompatible clones should enable to replace the current method of out-breeding and clonal propagation into an F 1 hybrid system with true seeds. This idea is not new, but has long been considered unrealistic. Severe inbreeding depression and selfincompatibility in diploid germplasm have hitherto blocked the development of inbred lines. Back-crossing with a homozygous progenitor with the Sli gene which inhibits gametophytic self-incompatibility gave self-compatible offspring from elite material from our diploid breeding programme. We demonstrate that homozygous fixation of donor alleles is possible, with simultaneous improvement of tuber shape and tuber size grading of the recipient inbred line. These results provide proof of principle for F 1 hybrid potato breeding. The technical and economic perspectives are unprecedented as these will enable the development of new products with combinations of useful traits for all stakeholders in the potato chain. In addition, the hybrid's seeds are produced by crossings, rendering the production and voluminous transport of potato seed tubers redundant as it can be replaced by direct sowing or the use of healthy mini-tubers, raised in greenhouses.

The Double-Reduction Landscape in Tetraploid Potato as Revealed by a High-Density Linkage Map

“…One consequence that has been described is its potential to lead to a higher inbreeding coefficient in dihaploids derived from tetraploid lines (Haynes and Douches 1993). Given the efforts currently underway toward hybrid potato breeding (Lindhout et al 2011), DR may have unwanted impacts on genetic diversity at the diploid level if future diploid founder material is derived from tetraploid lines. However, hybrid breeding depends on the production of highly homozygous inbred lines.…”

Overview and Breeding Strategies of Table Potato Production in Sweden and the Fennoscandian Region

“…Potato breeding has traditionally involved making crosses between pairs of parents with complementary features based on phenotype (Bradshaw and Bonierbale 2010). Diploid breeding may also lead to developing true F 1 hybrid potato seed derived from crossing non-related self-compatible homozygous diploids (Lindhout et al 2011). …”

Genetic mapping in polyploids

“…One consequence that has been described is its potential to lead to a higher inbreeding coefficient in dihaploids derived from tetraploid lines (Haynes and Douches, 1993). Given the efforts currently underway towards hybrid potato breeding (Lindhout et al, 2011), DR may have unwanted impacts on genetic diversity at the diploid level if future diploid founder material is derived from tetraploid lines. On the other hand, hybrid breeding is dependent on the production of highly-homozygous inbred lines.…”

“…Because of these and related difficulties, the use of polyploids in breeding programs is sometimes viewed as an unnecessary complication. Efforts to convert potato from a highly-heterozygous outbreeding polyploid to an inbreeding, homozygous diploid are currently underway (Lindhout et al, 2011;Jansky et al, 2016). In sugar beet (Beta vulgaris L.) breeding, the use of tetraploid parental lines has been largely abandoned (Dewey, 1980;Draycott, 2008) because of difficulties in autopolyploid breeding.…”

“…We have seen that inbreeding is not a practical proposition at the polyploid level (Haldane, 1930); it therefore seems we might have to "clean" polyploids at the haploid or diploid level by exposing deleterious mutations to selection. However if we were to go that route, returning to the polyploid level might not be needed (Lindhout et al, 2011;RennyByfield and Wendel, 2014;Jansky et al, 2016). Reducing genetic load at the polyploid level might be aided by genomic tools but it would take a significant (and perhaps unrealistic) effort to pinpoint all such loci, over multiple traits, and exclude them from future breeding germplasm using marker data.…”